a) Field of the Invention
The invention relates to a shaft reactor for treating bulk material, in particular, for the post-condensation of poly(ethylene terephthalate) (PET), poly(ethylenenaphthalate) (PEN) or polyamides (PA) in the solid phase (SSP process), but which is also applicable to the drying of other bulk materials, including granular bulk materials, and the like.
b) Description of the Related Art
Processes and apparatuses for crystallization and post-condensation of PET are adequately known. The post-condensation of PET is conventionally formed in solid phase at temperatures above 200.degree. C. for a period of a plurality of hours in reactors or dryers suitable therefor. The problem is to achieve a highest possible throughput of polyester material of high quality with the lowest possible consumption of energy and use of equipment. The process gas heats the polyester granules evenly and removes reaction products such as EG, water, etc., in which case agglutinations need to be avoided.
To achieve as uniform a countercurrent gas flow as possible, roof-shaped internals are frequently mounted in the preheater which additionally even out the product flow and decrease the bulk pressure, as is described, e.g., in DE-A-4300913.
The fabrication costs for the manufacture of such roof-type dryers are correspondingly high.
DE-C-2753549 describes an agglutination-free SSP process in a moving bed in a shaft reactor. In this case, net-like wire mesh cloths are arranged horizontally in the interior of the reactor at right angles to the reactor wall. The mesh width of the wire cloths is 4-6 times that of the granule size. Tendency to agglutinate, the migration velocity and reaction temperature of the polymer granules determine the spacing between two cloths.
The wire mesh cloths can also be formed in the manner of a chessboard, alternating or star-shaped. However, a disadvantage of this solution is the frequently unilateral product decrease or the non-uniform residence time in the reactor.
The fabrication costs are also high in the case of this solution and the cloths must be matched to the polymer material. All conventional displacement bodies, cones and the like cause a decrease of the usable contents of the reaction.